1. Field of the Invention
This invention relates to the processing of semiconductor wafers for the purpose of producing integrated circuits and the like, and particularly to a specialized technique useful in such production.
The present invention provides a measurement technique that makes for extremely efficient processing of semiconductor wafers because it enables the prediction of their propensity for oxygen precipitation, and thereby their characterization for ultimate device purposes, prior to the application of any heat treatment that is conventionally utilized.
2. Background Art
A variety of studies have been conducted over the past thirty years or so on the various effects of oxygen as an impurity in the processes of growing semiconductor crystalline bodies. For background material reporting on such studies, reference may be made for example to an article by W. Kaiser in Physical Review, Vol. 105, page 1751 (1957) and to an article by Kaiser and Keck in the Physical Review, Vol. 28, No. 8, page 882 (Aug. 1957).
Although the aforenoted studies establish the fact that the final resistivity obtained for a substrate or crystalline body depends on the oxygen contents of that body because of the well known phenomenon of generation of thermal donors, nevertheless there has been no technique developed in the art for predicting with accuracy the final profile of oxygen precipitation that will be obtained in a given wafer.
Accordingly, it is a primary object of the present invention to provide a technique that, by resistivity measurements taken prior to any heat treatment, will enable efficient characterization of wafers.
Another object of the invention is to apply the technique in such a way as to feed back the resistivity information obtained to the crystal growing activity, whereby appropriate modifications can be made in the crystal growth operation so as to correct undesired characteristics.
Another object is to utilize the discovery of the present invention as a sorting or screening device for the manufacturing process whereby certain wafers that have undesirble characteristics can be ruled out for further processing; alternately, the technique can be employed simply to characterize the various wafers that are encountered so that they can be appropriately utilized. In other words, those wafers that would normally be ruled out for the more general case, and thereby eliminated, would instead be retained, even though they did not possess the desired uniform resistivity pattern. Thus, wafers having apparently undesirable characteristics would be classified precisely for possible later use.